[31.06] Frequency of Weak Stellar Showers of Oort Cloud Comets

We have developed a semi-analytic model of the combined
effects of tidal perturbations of the galactic force and a
stellar impulse acting on the Sun and the outer Oort cloud
of comets. The six dimensional phase space of near-parabolic
comet orbital elements has been subdivided into cells. A
mapping of the evolution of these elements from beyond the
loss cylinder boundary into the inner planetary region over
the course of a single orbit is possible. The time
dependence of the comet flux interior to 5 AU is then
obtained for a period of 5 Myr subsequent to the impulse.
The peak flux and the time integrated net shower flux are
obtained over a wide range of stellar impact parameters
bsolar > 30 000 AU and stellar mass to relative
velocity ratios, M*/Vrel, such that the peak flux
enhancement is <1.5 times the background flux due to the
galactic tide alone. Loci of the results for the peak flux
enhancement and the time integrated net shower flux versus
bsolar and M*/Vrel are given. Using the number
densities and dispersion velocities of stellar populations
we also obtain the time dependent probability of a stellar
impulse versus bsolar and M*/Vrel. Finally, we
employ Monte Carlo sampling to estimate the frequency of
stellar encounters as functions of the peak flux enhancement
and also of the time integrated net shower flux. A graph of
the cumulative number of stellar impulses expected over 4
Gyr as a function of the shower strength will also be given.

\em{JJM acknowledges the support of a NASA-AAS Small
Research Grant and a NASA-ASEE Summer Faculty Fellowship at
Ames Research Center. JJL received support from Planetary
Geology and geophysics grant 334-30-50-01}

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